MISSISSIPPI EXPERIMENT STATION. 39 



siderably smaller than the compound Kohlrabi bundles. In the hybrid, 

 the bundles are intermediate in size and shape, being slightly nearer 

 the Radish bundle in size, and the Kohlrabi bundle in shape. 



Taking up the structure of the petiole in more detail we notice 

 that the epidermal cells have a thick cutinized outer wall about 6 - 9m 

 thick in each of the three plants. Just under the epidermal cells in 

 the Radish petiole there are 1-6 layers of coUenchyma cells, there 

 being only one layer most of the way around; in Kohlrabi there are 

 2-11 layers of these cells, 2-3 most of the way around, except at the 

 angles, where there are more ; in the hybrid there is but one well defined 

 layer most of the way around. The greater part of the mid-rib in each 

 plant is made up of sub-spherical, thin- walled parenchyma cells; in 

 Radish these cells are 150 - 200m in diameter, diminishing somewhat in 

 size toward the periphery ; in Kohlrabi they average about 75m in diam- 

 eter; in the hybrid they average 135m in diameter, and become slightly 

 smaller toward the periphery. 



As was stated above, the large vascular bundles in the mid-rib 

 of Radish, or the compound bundles in Kohlrabi and the hybrid appear 

 crescent-shaped in cross-section. In the central part of the mass of 

 tissue within the horns of the crescent is a mass of sclerenchyma tissue 

 which is made up of cells 12 - 21m in diameter, with walls thickened 

 tiniformly and strongly lignified. The corresponding cells in Kohlrabi 

 are parenchymatous with a slight indication of the beginning of the 

 formation of collenchyma tissue; in the hybrid, well developed coUen- 

 chyma tissue fills this space. In Kohlrabi and in the hybrid, rays of 

 these cells extend out between the parts of the compound bundle, thus 

 simulating medullary rays. The xylem in each plant consists of num- 

 erous annualar and spiral vessels and xylem parenchyma cells; and in 

 the Radish, the vessels average 33m in diameter; in Kohlrabi they are 

 some larger, being about 45m in diameter, while in the hybrid they are 

 about 36m wide. Fascicular cambium is well developed in the bundles 

 of each; it consists of several layers of brick-shaped cells, each being 

 about 5m wide and 15m long. Sieve tubes and companion cells are prom- 

 inent in the phloem of each plant, and are of about the same size in 

 each. In Radish, there is a layer of sclerenchyma tissue 100m wide, 

 bounding the phloem on the outer side; this is made up of cells similar 

 to the sclerenchyma cells in the central part of the bundle. Kohlrabi 

 and the hybrid have, corresponding to this tissue, strands of collen- 

 chyma tissue peripheral to each part of the compound vascular bundle . 



Leaf Lamina Structure: The entire thickness of the Radish 

 leaf lamina is 330m (sections taken in the central part of the leaf blade 

 at one side of the mid-rib) ; Kohlrabi leaf has a thickness of 300z and 

 the hybrid leaf 360m. The lower epidermal cells of Radish leaf are 

 about 15m thick (in direction perpendicular to leaf surface), and have a 

 rather thin outer wall, it being less than 2m in thickness; the upper 

 epidermal cells have about the same thickness with a slightly thicker 

 outer wall, it being 2 - 3m in thickness. On either side of the leaves of 

 Kohlrabi, the epidermal cells are 21 - 25m thick, and have an outer wall 

 3m thick. In the hybrid, the epidermal cells average about 22m in thick- 

 ness, and have an outer wall thickness of 3 - 6m. 



